Warfarin Management for PE and DVT
Target INR Range
For patients with pulmonary embolism (PE) or deep vein thrombosis (DVT), warfarin should be dosed to maintain an INR between 2.0 and 3.0, with a target of 2.5. 1, 2, 3
- This target range applies to all treatment durations for venous thromboembolism 3, 4
- An INR greater than 4.0 provides no additional therapeutic benefit and significantly increases bleeding risk 3
Initial Warfarin Dosing
Start warfarin at 5-10 mg daily for the first 2 days, then adjust based on INR response. 1, 2
Dosing Algorithm:
- Standard patients: 5-10 mg daily for first 2 days 1, 2
- Elderly or debilitated patients: Consider lower initial dose of 2-5 mg daily 3
- Patients with genetic variations (CYP2C9, VKORC1): Start with lower doses (2-4 mg) 3
- Loading doses are not recommended as they increase hemorrhagic complications without providing faster protection 3
Maintenance Dosing:
Critical Concurrent Heparin Therapy
Warfarin must be started simultaneously with therapeutic heparin anticoagulation, and heparin must be continued for at least 5 days AND until INR ≥2.0 for at least 24-48 hours. 1, 2, 4
Heparin Bridging Protocol:
- Unfractionated heparin: 80 IU/kg IV bolus, then 18 IU/kg/hour infusion 2, 6
- Target aPTT: 1.5-2.5 times control (45-75 seconds) 2, 6
- Minimum overlap: 5 days of heparin therapy 1, 2, 4
- Discontinuation criteria: INR ≥2.0 on two measurements at least 24 hours apart 2
Common Pitfall: Discontinuing heparin too early before adequate oral anticoagulation is the most frequent error—ensure both the 5-day minimum AND therapeutic INR criteria are met before stopping heparin. 1, 2
INR Monitoring Schedule
Initial Phase:
- First week: Check INR every 1-2 days until stable in therapeutic range 1
- After dose adjustments: Recheck INR within 6-10 hours 6
Maintenance Phase:
- Once stable, monitoring intervals can be extended gradually 1
- Maximum interval: Every 4-6 weeks for patients with consistently stable INR values 3, 5
- Patients with unstable INR require testing 2-4 times weekly 5
Treatment Duration
The duration varies based on clinical scenario 3, 4:
- Provoked DVT/PE (transient risk factor): 3 months 3, 4
- First unprovoked DVT/PE: At least 6-12 months, consider indefinite therapy 3, 4
- Recurrent DVT/PE: Indefinite treatment 3
- Cancer-associated VTE: At least 3 months, continue as long as cancer is active 4
Special Considerations
Age-Related Adjustments:
- Patients over 62 years may benefit from a narrower target range of 2.0-2.5 to reduce major bleeding risk 7
- Very elderly patients should start with 2-4 mg rather than 5 mg 3, 5
Evidence Quality Note:
The FDA label 3 and recent guidelines 1, 2 consistently support the 2.0-3.0 INR range, which is more effective than lower ranges (1.5-1.99) for preventing recurrent VTE without significantly increasing bleeding risk 7. The 5-10 mg starting dose is preferred over 3 mg, as it requires less dose adjustment to reach therapeutic levels 2, 8.